CN109211461B

CN109211461B - Capacitive pressure sensor for monitoring a building structure, in particular made of concrete

Info

Publication number: CN109211461B
Application number: CN201810732336.5A
Authority: CN
Inventors: F·帕帕拉多; A·彭尼西; E·圭德蒂; A·多里亚尼
Original assignee: STMicroelectronics SRL
Current assignee: STMicroelectronics SRL
Priority date: 2017-07-05
Filing date: 2018-07-05
Publication date: 2021-06-25
Anticipated expiration: 2038-07-05
Also published as: EP3425360A1; EP3425360B1; IT201700073763A1; US10914647B2; CN208833260U; CN109211461A; US20190011320A1

Abstract

The present application relates to a capacitive pressure sensor for monitoring building structures, in particular made of concrete. A capacitive sensor for monitoring stresses acting in a building structure and having a multilayer structure provided with an upper conductive layer defining an upper outer surface of the sensor. The lower conductive layer defines a lower outer surface. At least a first structural layer of insulating material is in contact with the upper conductive layer and at least a second structural layer of insulating material is in contact with the lower conductive layer. At least a first slab is made of conductive material and at least a second slab is made of conductive material, at least one dielectric layer being interposed between the first slab and the second slab to define at least one detection capacitor inside the multilayer structure of the sensor. The upper conductive layer and the lower conductive layer together define an electromagnetic shield for shielding the detection capacitor to prevent electromagnetic interference originating from outside the capacitive sensor.

Description

Capacitive pressure sensor for monitoring a building structure, in particular made of concrete

Technical Field

The present solution relates to a capacitive pressure sensor for monitoring the condition of a building structure, such as a building, an infrastructure or the like.

Background

Reference is made below to building structures made of concrete as a preferred field of application. However, the present solution is in principle applicable to various types of structures or parts of structures, in particular those made of materials that are partly liquid or fluid at the time of manufacture or production and that are subsequently hardened therein, wherein the health and stress of these structures need to be monitored at any time.

It is well known that it is considered necessary to monitor and assess the health of structures such as tunnels, bridges or overpasses, produced by the construction industry, over time, in order to prevent the occurrence of cracks and accidents. In particular, the supported load and any particular stresses, forces or strains that may act on the material constituting the structure must be monitored.

Some current non-destructive evaluation (NDE) techniques use sensors, for example operating by mechanical, optical or magnetic principles, fixed outside the structure to be monitored, indirectly measuring the stresses acting on the structure, taking into account the stresses by correlating them with other measurable variables (tilt, deformation, etc.). For example, it has been proposed to use extensometers externally mounted on the structure to be monitored for indirect measurement of deformation.

However, in general, these sensors are bulky, costly and prone to error. Complex electronic interfaces are also typically required to process the acquired information and correlate it with the forces and stresses to be monitored.

Other known solutions provide for the use of suitable sensors, such as ceramic sensors, embedded in the structure to be monitored. However, in such cases, if the sensors are not adequately protected, they are often subject to humidity and/or other factors that can distort their results and/or shorten their useful life. Furthermore, the positioning of these sensors is often critical and in particular they can become partially separated from the material of the structure to be monitored (a process known as stratification), for example due to the presence of sand, gravel or air bubbles trapped in the concrete structure, which can interfere with the sensors.

In general, the large-scale use of sensors applied to buildings and civil engineering structures requires the development of innovative sensors capable of meeting one or more of the following requirements: the precision is high; high robustness; the cost is low; high resistance to electromagnetic interference that may distort the detection results; simplification and stabilization of positioning; the operation is simplified; and good surface adhesion of the structure to be monitored.

In particular, requirements regarding resistance to electromagnetic interference have found that in the environment monitored by sensors, in particular during the construction of the structure to be monitored, there are generally electric motors generating high magnetic fields when in use, including for example excavators, machines for extracting materials, hydraulic pumps, etc.

Disclosure of Invention

The present disclosure provides a sensor for monitoring a building structure that overcomes at least some of the disadvantages of the prior art and meets the needs and requirements of the industry.

According to the present disclosure, there is provided a capacitive pressure sensor as defined in the appended claims.

Drawings

In order that the disclosure may be more readily understood, preferred embodiments thereof will now be described, purely by way of non-limiting example, with reference to the accompanying drawings, in which:

fig. 1A is a schematic representation in plan view of a capacitive pressure sensor according to an embodiment of the present solution;

FIG. 1B is a cross-sectional view of the sensor of FIG. 1A;

FIG. 2 is an equivalent electrical diagram of the capacitive pressure sensor of FIGS. 1A and 1B;

3A-3B are schematic top views of alternative embodiments of capacitive pressure sensors of the present disclosure;

fig. 4-5 are cross-sectional views of other variations of capacitive pressure sensors according to embodiments of the present disclosure;

fig. 6A is a cross-sectional view of a capacitive pressure sensor according to another embodiment of the present solution;

FIG. 6B is a layout view of a first plate layer of the sensor of FIG. 6A;

FIG. 6C is a layout view of the lower metal layer of the sensor of FIG. 6A;

FIG. 7 is a schematic representation of a capacitive pressure sensor secured to a support structure, particularly a cage for concrete construction, according to one embodiment of the present disclosure;

fig. 8A is a cross-sectional view of a capacitive pressure sensor according to yet another embodiment of the present solution;

FIG. 8B is a layout view of the upper metal layer of the sensor of FIG. 8A;

FIG. 8C is a layout view of a first plate layer of the sensor of FIG. 8A;

FIG. 8D is a layout view of a second plate layer of the sensor of FIG. 8A;

FIG. 8E is a layout view of the lower metal layer of the sensor of FIG. 8A;

FIG. 9 is a cross-sectional view of the sensor of FIG. 8A, showing electric field lines associated with the corresponding detection capacitors;

10A-10B are schematic representations of electrical connections between capacitive pressure sensors and corresponding measurement circuitry according to embodiments of the present disclosure;

FIG. 11A is a cross-sectional view of a capacitive pressure sensor in accordance with yet another embodiment of the present solution;

FIG. 11B is a layout view of the upper metal layer of the sensor of FIG. 11A;

FIG. 11C is a layout view of a first plate layer of the sensor of FIG. 11A;

FIG. 11D is a layout view of a second plate layer of the sensor of FIG. 11A;

FIG. 11E is a layout view of the lower metal layer of the sensor of FIG. 11A;

FIG. 12 is a layout view of the plates of another variation of a capacitive pressure sensor according to an embodiment of the present disclosure;

fig. 13A-13B are cross-sectional views of yet another variation of a capacitive pressure sensor according to an embodiment of the present disclosure;

FIG. 14A is a cross-sectional view of another variation of a capacitive pressure sensor according to an embodiment of the present disclosure;

FIG. 14B is a schematic plan view of the sensor of FIG. 14A;

FIG. 15 shows a graph of electrical quantities associated with a capacitive pressure sensor in accordance with an embodiment of the present disclosure; and

fig. 16 shows a plan view of a set of basic cells of a capacitive pressure sensor according to an embodiment of the present disclosure, according to another aspect of the present solution.

Detailed Description

The applicant has first found that a capacitive sensor with flat parallel sheets or plates (known as PPCS, parallel plate capacitor sensor) can have the characteristics of being able to meet the requirements for stress detection within building structures, in particular concrete structures, and of providing a high sensitivity to small relative movements between the plates (due to the stresses to be monitored), the possibility of coupling to standard electronic interfaces, a high configurability to adapt to the different detection requirements, and a high adhesion to the material of the structure to be monitored, minimizing the risk of separation, and minimizing the possibility of interference of bubbles, sand, gravel or other rough areas in the structure.

As will now be described in detail, the present solution provides a technical production arrangement to ensure that a flat parallel plate capacitive sensor operates correctly as an optimized pressure sensor in a structure to be monitored, in particular in a concrete structure.

Fig. 1A and 1B show in plan view and in section, respectively, a general detection structure of a capacitive pressure sensor of the flat parallel plate type according to an embodiment of the present solution, which can be used to monitor the condition of a concrete structure (not shown) when inserted into the structure in question. As described below, the structure is formed by techniques for semiconductor materials, particularly for Printed Circuit Boards (PCBs).

The capacitive sensor, indicated as a whole with 1, comprises a first outer metal layer 2a, for example made of copper or other conductive material, having a planar extension in a horizontal plane xy, and a second outer metal layer 2b, also for example made of copper or other conductive material, having a planar extension in the horizontal plane xy. With respect to the direction of the vertical axis z orthogonal to the horizontal plane xy, the first outer metal layer 2a may be regarded as an upper metal layer (and referred to as an upper metal layer hereinafter), and the second outer metal layer 2b may be regarded as a lower metal layer (and referred to as a lower metal layer hereinafter).

The capacitive sensor 1 further comprises a first plate layer 4a between the upper metal layer 2a and the lower metal layer 2b, which first plate layer 4a is made of copper, for example, with a planar extension in a horizontal plane xy. A first structural layer 5a, for example made of an insulating material of glass ceramic, Vetronite or FR-4 (composite material consisting of glass fibres bonded together with epoxy resin), is inserted in contact between the upper metal layer 2a and the first sheet layer 4 a. The second sheet layer 4b is also made of copper, for example, with a planar extension in the horizontal plane xy, and the second structural layer 5b is also made of an insulating material, for example of glass ceramic, Vetronite or FR-4, interposed in contact between the lower metal layer 2b and the second sheet layer 4 b.

The capacitive sensor 1 further comprises a dielectric layer 6, the dielectric layer 6 having a planar extension in the horizontal plane xy and being interposed between the first 4a and the second 4b plate layer so as to form a detection capacitor C having a flat parallel plane, the plates of which are defined by the first 4a and the second 4b plate layer.

Thus, the capacitive sensor 1 has a multilayer structure, in which the layers are stacked in the direction of the vertical axis z, which defines within itself a detection capacitor C by means of the first 4a and second 4b plate layers and the interposed dielectric layer 6.

The capacitive sensor 1 further comprises a first contact element 8a made of an electrically conductive material (for example copper), the first contact element 8a electrically contacting the first plate layer 4a and in particular the plate of the detection capacitor C defined by the first plate layer 4 a.

In the example shown, the first contact element 8a extends vertically through the entire thickness of the first structural layer 5a, in contact with the first ply 4 a. A first contact opening 9a is formed through the upper metal layer 2a at the location of the first contact element 8a and allows an electrical contact to be provided to the first plate layer 4a from the outside to define a first plate electrode a of the capacitive sensor 1.

Similarly, the capacitive sensor 1 comprises a second contact element 8b, made of an electrically conductive material, for example also copper, which extends vertically through the entire thickness of the second structural layer 5b and electrically contacts the second plate layer 4b, in particular the plate of the detection capacitor C defined by the second plate layer 4 b. A second contact opening 9B is formed through the lower metal layer 2B at the location of the second contact element 8B and allows an electrical contact to be provided from the outside to the second plate layer 4B to define a second plate electrode B of the capacitive sensor 1.

In the embodiment shown, the first and

second contact elements

8a, 8b and the first and

second contact openings

9a, 9b have a circular cross-section in the horizontal plane xy, the diameter of the circular cross-section of the

contact openings

9a, 9b being larger than the respective diameter of the circular cross-section of the first and

second contact elements

8a, 8 b. The aforementioned first 8a and second 8b contact elements are also centrally located with respect to the entire structure of the capacitive sensor 1.

As also shown in fig. 2, which shows an equivalent circuit representation of the capacitive sensor 1, the same capacitive sensor 1 further comprises a shielding electrode S, which electrically contacts the upper metal layer 2a and the lower metal layer 2b, which together form an outer shield to shield the capacitive sensor 1 against electromagnetic interference, thereby insulating the interior of the capacitive sensor 1, in particular the detection capacitor C, from electromagnetic interference.

In use, the capacitive sensor 1 detects a pressure P acting on the capacitive sensor 1 in the normal direction (along the vertical axis z). This pressure P causes a variation of the distance d between the plates of the detection capacitor C, i.e. a variation of the distance d between the first 4a and second 4b plate layers, which in turn is due to a variation of the thickness of the corresponding dielectric layer 6. Thus, there is a change in the capacitance of the detection capacitor C, indicating the pressure P to be detected.

For example, if the pressure P generates a compressive stress, the thickness of the dielectric layer 6 decreases, and the distance d between the first plate layer 4a and the second plate layer 4b of the capacitive sensor 1 also decreases.

The value of the dielectric constant of the dielectric layer 6, the rest value of the distance d and/or the dimensions of the first 4a and second 4b slab in the horizontal plane xy may be chosen in a suitable way in order to obtain the desired sensitivity of the capacitive sensor 1 with respect to the pressure P to be detected, and generally with respect to the stress to be monitored.

In particular, the capacitive sensor 1 can be designed to be sensitive only to the normal component of the pressure P, without any horizontal component of the pressure P causing a significant change in the capacitance of the detection capacitor C.

As mentioned above, the upper and

lower metal layers

2a, 2b may be connected to a suitable reference potential (such as ground or ground potential) by means of the shielding electrode S, so as to form a shield to prevent electromagnetic interference, for example generated by a motor operating in the working environment of the capacitive sensor 1 (the shield forming a sort of faraday cage in which the detection capacitor C is placed). Thus, the operating state of the capacitive sensor 1 can also be monitored during the installation phase and rapid action can be taken, for example in the event of breakage or malfunction.

According to a particular aspect of the present solution, as schematically illustrated in fig. 1A and 1B, the capacitive sensor 1 further comprises a suitable number of supports or standoffs 10 coupled to the upper metal layer 2a and/or the lower metal layer 2B outside the structure of the capacitive sensor 1.

Each of the brackets 10 has a coupling portion 10a for coupling to an outer surface of the corresponding upper metal layer 2a or lower metal layer 2 b. The body part 10b and the head part 10c are, for example, substantially parallel to the horizontal plane xy, the body part 10b extending from the outer surface of the respective upper metal layer 2a or lower metal layer 2b in the direction of the vertical axis z, and the head part 10c being connected to the body part 10b and extending transversely to the body part 10b and the vertical axis z.

The extension and shape of the coupling portion 10a of the holder 10 in the horizontal plane xy may be of various types, for example circular or rectangular. Similarly, the shape of the body portion 10b may be of different types, for example in the form of a parallelepiped or a truncated pyramid or cone.

In the illustrated embodiment, the stent 10 is coupled to the surface of the respective upper or

lower metal layer

2a, 2b at respective lateral perimeter portions, for example at four lateral perimeter portions arranged at substantially the same distance from the geometric center of the upper and

lower metal layers

2a, 2b in the horizontal plane xy.

Alternatively, as described below, a single support 10 may be provided, which is coupled to the respective upper or

lower metal layer

2a, 2b in a suitable manner, for example in the centre of the layer.

The presence of the support 10 makes the capacitive sensor 1 sensitive not only to the compressive stresses that generate a pressure P on the respective upper and lower metal layers 2a, 2B, but also to the tensile stresses that generate a counter-pressure P' on the upper and lower metal layers 2a, 2B (see fig. 1B).

The bracket 10 also forms a suitable element for attaching or adhering the capacitive sensor 1 to the material of the structure to be monitored (e.g. concrete), thereby reducing the risk of separation or delamination.

In particular, the presence of the support 10 ensures that the capacitive sensor 1 operates correctly even in the presence of air bubbles or other impurities (for example sand or gravel) within the structure to be monitored.

As shown in fig. 3A and 3B, the shape in the horizontal plane xy of the upper and lower metal layers 2a, 2B of the capacitive sensor 1 (and therefore the outline of the capacitive sensor 1 in the horizontal plane xy) may be, for example, square (fig. 3A) or circular (fig. 3B), instead of rectangular (as shown in fig. 1A described earlier).

Fig. 4 shows a possible variant of the capacitive sensor 1, in which the corresponding stacked multilayer structure comprises a greater number of stacked layers.

In particular, in this case, the capacitive sensor 1 comprises a further dielectric layer 6', a third 4c and a fourth 4d plate layer and a third structural layer 5 c.

In this case, the second 4b and third 4c plate layers are electrically connected to one another by means of the transverse connecting

elements

8c, 8d, so that they together form a central plate, and the third structural layer 5c is inserted between the second 4b and second 4c plate layers in the center of the multilayer structure. The third plate layer 4c and the fourth plate layer 4d with the further dielectric layer 6' inserted therein form a further detection capacitor.

The

transverse connection elements

8c, 8d are in electrical contact via further plate electrodes in this case and are also coupled to further supports 10', which in this case extend transversely with respect to the stacked structure of the capacitive sensor 1. The presence of these further supports 10' ensures that the central plate of the capacitive sensor 1 is substantially fixed with respect to the pressure P to be detected.

In this embodiment, the capacitive sensor 1 is capable of detecting not only the amount of pressure P acting in the direction of the vertical axis z, but also the direction of this pressure along the vertical axis z, or is capable of determining whether the pressure acts above or below the capacitive sensor 1 (assuming that in this case, different variations in the capacitance of the detection capacitor occur above and below the vertical axis z. it should be noted that in this case, the corresponding plate electrode A' is provided for electrical connection of the fourth plate layer 4 d).

As shown in fig. 5, the stacked structure of the capacitive sensor 1 may comprise an even greater number of stacked layers, and in particular further dielectric layers 6' and further plate layers, here generally indicated with 14, inserted and interleaved with each other to form further detection capacitors.

In the example shown in fig. 5, the capacitive sensor 1 comprises five detection capacitors, formed by the respective plate layers 4a-4d, 14 and the dielectric layers 6, 6'. Additionally, in this example, the plate layers 4a-4d, 14 are alternately (along the direction of the vertical axis z) electrically connected to each other by respective transverse connecting elements 8C, 8d, so that the detection capacitors are connected in parallel to each other to form a single resulting detection capacitor C between the first plate electrode a and the second plate electrode B.

It is, however, obvious that different connections can be made in series in the detection capacitor, for example. It is also possible to provide the various dielectric layers 6, 6' with different dielectric materials.

A specific embodiment of a capacitive sensor 1, which is particularly suitable for monitoring building structures made of concrete, such as tunnels, will now be described first with reference to fig. 6A and 6B to 6C, in which case the capacitive sensor 1 is intended to be embedded within a basic structural element (such as a block) of the building structure.

In this embodiment, the capacitive sensor 1 is formed by the stacking of two double-sided multilayer sheets, indicated by 15a, 15b, with the interposition of a dielectric layer 6, in this case the dielectric layer 6 being made of Kapton as dielectric material (advantageously a material with high thermal stability).

Each of these

sheets

15a, 15b is formed by a core of insulating material (in this case FR-4) covered on two main external faces (upper and lower) by a conductive covering sheet or layer, in particular a copper layer. For example, the conductive cover layer has a thickness of 35 μm and the

entire sheet

15a, 15b has a thickness of 1.6mm (it should be noted that the drawings are obviously not drawn to scale for clarity of illustration).

Thus, the structure of the

sheets

15a, 15b is completely similar to that of a double-sided Printed Circuit Board (PCB). In this case, therefore, the method for forming the capacitive sensor 1 can advantageously use a common printed circuit board manufacturing method, as will be apparent to those skilled in the art.

FR-4 has a Young's modulus of about 24GPa and a maximum dielectric constant of 4.7 (which is, for example, 4.35 at a frequency of 500MHz and 4.34 at a frequency of 1 GHz), and Kapton has a Young's modulus of about 2.5GPa and a dielectric constant of 3.5 at a frequency of 1 kHz.

In detail, as shown in fig. 6A, the first sheet 15a placed on top in the stacked structure of the capacitive sensor 1 thus defines the upper metal layer 2a, the first structural layer 5a and the first plate layer 4 a. Similarly, the second sheet 15b placed at the bottom in the stacked structure of the capacitive sensor 1 defines the lower metal layer 2b, the second structural layer 5b and the second plate layer 4 b.

For example, the dielectric layer 6 may have a thickness of between 25 μm and 100 μm (for clarity of illustration, it should be emphasized again that the figures are not drawn to scale). The dielectric layer 6 may be made in a modular manner, for example by stacking an appropriate number of Kapton sheets, each having a thickness of 25 μm.

In a manner not shown, a filling and adhesion layer may also be provided between the metal layer and the dielectric layer, such a layer being referred to as a "prepreg" layer, as is well known in the art of printed circuit board manufacturing.

According to one aspect of the present solution (reference should also be made to fig. 6B, showing the layout of the first plate layer 4a, seen from the direction of the upper metal layer 2 a), the first plate layer 4a (in this case carried by the first sheet 16 a) is suitably shaped so as to define the active area 17 of the capacitive sensor 1, that is to say the shape and dimensions of the first plate of the corresponding detection capacitor C.

In particular, the first trench 18 is formed through the entire thickness of the first slab 4a (and, if necessary, through a portion of the first structural layer 5 a) so as to define and separate an active portion 19 of the first slab 4a inside the first trench 18 in the horizontal plane xy and an outer portion 20 of the first slab 4a outside the first trench 18.

In the example shown, the first trench 18, which is empty inside, is substantially annular and the active portion 19, which defines the first plate of the detection capacitor C, has a substantially circular shape in the horizontal plane xy.

In the embodiment shown, the shape of the capacitive sensor 1 is also substantially circular in the horizontal plane xy. In particular, in this example, the diameter of the active portion 19 (that is to say of the plates of the detection capacitor C) may be between 20mm and 26mm, while the external diameter of the overall structure of the capacitive sensor 1 may be between 37mm and 47mm (it should be noted that these dimensions are provided purely by way of example).

According to another aspect of the present solution, the trench 18 has an extension 18', the extension 18' extending along the horizontal axis of the horizontal plane xy (in this example along the y-axis), and also defining an electrical connection portion 22 from the first plate layer 4a, which extends from the active portion 19 and through the outer portion 20 of the first plate layer 4a, and in this example as far as the outer lateral edge of the first plate layer 4a and of the entire structure of the capacitive sensor.

As shown in fig. 6C, an opening 24 is also formed at the aforementioned outer transverse edge of the first plate layer 4a, through the upper metal layer 2a and through the first structural layer 5a, so as to allow electrical connection to the electrical connection portion 22 (and therefore to the active portion 19 of the first plate layer 4a and the corresponding first plate of the detection capacitor C) by means of, for example, electrical wires placed transversely to the structure of the capacitive sensor 1. It should be noted that in this case, the electrical connection portion 22 has a similar function to the contact element 8a defined above with reference to fig. 1B, since it contributes to the definition of the first plate electrode a and allows electrical connection to the first plate of the detection capacitor C.

It is evident that in this case too, the electrical connection to the second plate of the detection capacitor C (formed by the second plate layer 4 b) can be formed transversely to the structure of the capacitive sensor 1.

As shown in fig. 6B and 6C, the capacitive sensor 1 further comprises fastening through holes 26, three in this example, which pass through the entire thickness of the multilayer structure of the capacitive sensor 1. The interior of the fastening through-hole 26 is conveniently plated, for example with copper.

The fastening through-holes 26 may for example be placed at the vertices of a regular triangle inscribed in the outer portion 20 of the first slab 4a (and similarly through the other stacked layers).

As schematically shown in fig. 7, connection wires 29 may be introduced through these fastening through holes 26, which are rigid and/or elastic or partly elastic and may be used for fastening or attaching the capacitive sensor 1 to an external support or fastening structure 30, e.g. a cage made of iron or other material, for the casting of concrete and the production of a corresponding building structure 31, e.g. a block. The connection line 29 advantageously enables the capacitive sensor 1 to be positioned simply and stably when the connection line 29 is embedded in the building structure 31.

In another embodiment, as shown in fig. 8A (cross section) and fig. 8B to 8E (showing the layout of the upper metal layer 2a, the first plate layer 4a, the second plate layer 4B, and the lower metal layer 2B, respectively). In the capacitive sensor 1, the second plate layer 4b carried by the second sheet 15b is also suitably shaped so as to define the active area 17 of the capacitive sensor 1, that is to say the shape and dimensions of the second plate of the corresponding detection capacitor C.

In particular (see fig. 8D), the second groove 27 is formed through the entire thickness of the second ply 4b (and, if necessary, through a portion of the second structural layer 5 b) so as to define and separate an active portion 19 'of the second ply 4b inside the second groove 27 and an outer portion 20' of the second ply 4b outside the second groove 27 in the horizontal plane xy.

In the example shown, the second trench 27 is substantially annular and the active portion 19' of the second plate defining the corresponding detection capacitor C has a substantially circular shape in the horizontal plane xy.

In particular, the diameter of the active portion 19' defined in the second slab 4b in this case (purely by way of example, equal to 10mm) is smaller than the diameter of the corresponding active portion 19 defined in the first slab 4a (purely by way of example, equal to 11 mm). Therefore, in this case, the size of the effective capacitance detection area (indicated by the dashed box in fig. 8A) is defined by the size of the active portion 19' of the second plate layer 4 b.

Advantageously, this characteristic of the superposition (or "overlap") between the active portions 19, 19' makes the capacitive sensor 1 completely insensitive to the transversal component of the pressure P to be monitored acting along the direction of the horizontal plane xy. In fact, the stresses acting in this direction, even if they cause a relative movement between the two plates of the detection capacitor C, cannot in any case change the size of the effective detection area, which continues to be determined by the smaller of the two plates (also indicated by the aforesaid box indicated by the dashed line in fig. 8A). Similarly, this solution may ensure that any misalignment errors between the layers that may occur during the manufacture of the capacitive sensor 1 do not play a role.

As schematically shown in fig. 9, the presence of the

trenches

18, 27 in the two

plate layers

4a, 4b causes the electric field lines E at the edge of the detection capacitor C to be completely closed by the dielectric layer 6 and the outer portions 20, 20' of the plate layers 4a, 4 b. And in any case within the structure of the capacitive sensor 1, rather than being transmitted to the environment outside the capacitive sensor 1, that is to say into the material of the structure to be monitored (for example concrete, the precise dielectric properties of which are unknown, these properties possibly depending in particular on the moisture and components that may be present in such a material).

As shown in fig. 9, the capacitive sensor 1 may have an insulating coating 32, for example made of silicone, covering the entire outer lateral surface of the multilayer structure of the capacitive sensor 1, as required, so as to further improve the impermeability and the insulation of the capacitive sensor 1 with respect to moisture and other factors that may be present in the environment outside the capacitive sensor 1.

As shown in fig. 8D, the second trench 27 also has an extension 27', which extension 27' extends along the horizontal axis of the horizontal plane xy (in this example along the y-axis), defining from the second plate layer 4B a respective electrical connection portion 22', which electrical connection portion 22' extends from the active portion 19 'and reaches the outer portion 20' of the second plate layer 4B to allow an electrical connection to be provided from the outer lateral surface of the capacitive sensor 1 (defining the second plate electrode B).

As also shown in fig. 8B, 8E, the upper and lower metal layers 2a, 2B and the first and second structural layers 5a, 5B may have corresponding openings 24 for lateral access of electrical connection lines to the plates of the detection capacitor C.

In detail, the solution described herein may advantageously allow some variants of the plates electrically connected to the detection capacitor C via the first and second plate electrodes a, B and the shielding electrode S.

In a first variant, schematically illustrated in fig. 10A, the capacitance measurement, performed by a suitable measuring circuit 35 supplied with the supply voltage Vcc (i.e. between the two plates of the detection capacitor C, both plates being biased to a voltage other than the ground potential gnd of the measuring circuit 35), is insulated or differential. Therefore, the first board electrode a and the second board electrode B are both insulated from the ground gnd, and each board electrode is connected to a corresponding pole of the electrical connection cable. In this case, the shielding electrode S of the capacitive sensor 1 may be connected to the ground potential gnd, or, as in the illustrated example, to the ground potential, in line with a ground shield 36 of an electronic device 37 of which the measuring circuit 35 forms part.

In a second variant, schematically illustrated in fig. 10B, the measurement of the capacitance is unipolar or with respect to ground, that is to say one of the two plates of the detection capacitor C is connected to the ground potential gnd of the circuit. In this example, the first plate electrode a is connected to ground gnd, while the second plate electrode B is connected to a single pole of an electrical connection cable. Also in this case, the shielding electrode S of the capacitive sensor 1 may be connected to the ground potential gnd, that is, to the ground shield 36 of the electronic device 37.

A further embodiment of the capacitive sensor 1 will now be described with reference to fig. 11A (cross section) and fig. 11B to 11E (which show the layout of the upper metal layer 2a, the first plate layer 4a, the second plate layer 4B and the lower metal layer 2B, respectively).

This embodiment differs from the embodiment described above in that the electrical connection to the plates of the detection capacitor C is provided from a peripheral edge portion of the upper surface of the upper metal layer 2a (and/or the lower surface of the lower metal layer 2b) of the capacitive sensor 1 outside the active area 17 of the capacitive sensor 1 (in this case having a square or rectangular outline), rather than providing lateral access to the electrical connection lines.

In this case, a first connection hole 40 is provided (also called "via") which is plated on its inner wall (and insulated from the outside of the layer of the structure through which it passes). It extends, for example, from the upper surface of the upper metal layer 2a, through the upper metal layer 2a and the first structural layer 5a, and reaches the first slab layer 4a, where it terminates at an electrical connection portion 22 outside the active portion 19 of this first slab layer 4 a. As mentioned above, the electrical connection portion 22 reaches the active portion 19 of the outer portion 20 by following a suitable route through the first ply 4 a.

Similarly, a second connection hole 42 is provided. It also extends, for example, from the upper surface of the upper metal layer 2a, through the upper metal layer 2a, the first structural layer 5a, the first slab layer 4a and the dielectric layer 6, and to the second slab layer 4b, where it terminates at a respective electrical connection portion 22 'outside the active portion 19' of the second slab layer 4 b. As mentioned above, the electrical connection portions 22' reach the respective active portions 19' of the second ply 4b by following a suitable route from the outer portion 20 '.

First and second electrical contact pads 44a, 44B are provided on the aforementioned peripheral edge portion of upper metal layer 2a to allow electrical connection with the plates of detection capacitor C, thereby defining first and second plate electrodes a, B.

If desired (as shown in fig. 11B to 11E, but not in fig. 11A), the aforementioned first and second connection holes 40, 42 may continue through the remaining layers of the structure of the capacitive sensor 1 until they reach the lower surface of the lower metal layer 2B, wherein further electrical contact pads may be provided for making additional electrical connections from the lower surface of the capacitive sensor 1 to the plates of the detection capacitor C.

A third electrical contact pad 44c is also provided in a position adjacent to the aforementioned first and second

electrical contact pads

44a, 44b to define a shielding electrode S of the capacitive sensor 1.

A shield hole 43 (not shown in fig. 11A) is also provided and the shield hole 43 is also plated on its inner wall (and is externally insulated) from the upper surface of the upper metal layer 2a through the entire structure of the capacitive sensor 1 to the lower surface of the lower metal layer 2b, where additional electrical contact pads may be provided for electrical connection to the shield of the capacitive sensor 1, if desired.

In the illustrated embodiment, there are also plated through holes 45 that also pass through the entire structure of the capacitive sensor 1 and are positioned at uniform intervals along the entire lateral perimeter of the capacitive sensor 1. These plated through holes 45 collectively define an additional shield against electromagnetic interference that also laterally insulates and shields the detection capacitor C formed inside the structure of the capacitive sensor 1.

In this embodiment, fastening through holes 26 are also provided, which may also advantageously be internally plated.

Further through holes 46 may also be provided, which are for example evenly distributed outside the active area 17 of the capacitive sensor 1 and have the same cross section as the plated through holes 45 or a larger cross section. Advantageously, these internally plated further through holes 46 may contribute to the definition of the electrostatic shield and to the mechanical locking between the layers of the sensor (by virtue of the corresponding internal plating).

In a possible variant, schematically illustrated in fig. 12, one or more through-holes 48 can also be provided in the active region 17 of the capacitive sensor 1, if desired. This example shows a single via 48 centrally passing through the plate of the detection capacitor C defined by the active portion 17 of the first plate layer 4a (in this case having the shape of a resulting circular ring in the horizontal plane xy).

These through holes 48 are able to allow fluid communication between the upper and lower surfaces of the capacitive sensor 1, and may advantageously allow the passage of air, thus preventing the formation of bubbles that may adhere to the upper and lower surfaces of the capacitive sensor 1 and therefore hinder the correct detection of the pressure P to be monitored.

It will be appreciated by those skilled in the art that in all embodiments of the capacitive sensor 1, a support 10 having the above-described functionality may advantageously be provided (where this is not explicitly shown even for simplicity and clarity of illustration).

For example, as schematically shown in fig. 13A, only two supports 10 may be provided, which are centrally located, one on each of the upper and lower surfaces of the capacitive sensor 1, and are coupled to the upper and

lower metal layers

2a and 2b, respectively.

As shown in the example, these supports 10 may have a body portion 10b of parallelepiped or trapezoidal shape.

Alternatively, as schematically shown in fig. 13B, the main body portion 10B of the stand 10 may be pyramidal or conical (thereby providing a larger surface on the corresponding coupling portion 10a for coupling to the respective upper or lower metal layer 2a, 2B).

As shown in fig. 14A (cross section) and fig. 14B (showing the layout of the upper metal layer 2a, or similarly, the layout of the lower metal layer 2B), various supports 10 may be provided for each of the upper and lower surfaces of the capacitive sensor 1. In this example, four supports 10 located on the periphery of the active area 17 of the capacitive sensor 1 and one support 10 located in the center of the active area 17 of the capacitive sensor 1 are provided.

The advantages of the solution are evident from the foregoing description.

In any case, it should be stressed again that this solution makes it possible to produce sensors, for example for applications in buildings and civil engineering structures, which are able to meet one or more of the following requirements: the measurement precision is high; high robustness; the cost is low; high resistance to electromagnetic interference that may distort the detection results; simplification and stabilization of positioning; the operation is simplified; and good surface adhesion of the structure to be monitored.

Experimental tests and experiments carried out by the applicant have verified the accuracy of the measurements provided by the capacitive sensor 1 under practical use conditions for monitoring high values of effective stress (operating range up to limits of, for example, 500 atm) which may reach hundreds of atmospheres.

For example, fig. 15 shows a graph of the pressure values detected by the capacitive sensor 1 in the detection time interval T, in which case the capacitive sensor 1 is embedded in a concrete block. The corresponding values of the capacitance of the sensing capacitor C are also shown.

As shown in the graph, the value detected by the capacitive sensor 1 (shown by the solid line) reproduces the theoretical value or the expected value (shown by the broken line) with a high level of accuracy. In particular, as indicated in the portion of the graph in the circular frame, the capacitive sensor 1 is advantageously also able to detect a negative pressure value if there is a counter-pressure stress acting in the monitored structure.

Additionally, as mentioned above, the capacitive sensor 1 may advantageously be produced by Printed Circuit Board (PCB) manufacturing techniques. Thus, the sensor is fast and economical to manufacture.

On this subject, fig. 16 shows by way of example a complete slab 50' comprising a plurality of elementary cells 50 of the capacitive sensor 1 as a starting point from which the various elementary cells 50 can be separated from one another to produce a corresponding capacitive sensor 1.

Finally, the solution described and illustrated herein can be easily modified and varied without departing from the scope of protection of the present disclosure, as defined in the appended claims.

For example, the materials used to produce the capacitive sensor 1 may be different from those shown above. Similarly, further variant shapes may be provided for the structure of the capacitive sensor 1.

In particular, the materials forming the structural layers of the

sheets

15a, 15b and of the dielectric layer 6 may be different from those mentioned, namely FR-4 and Kapton, since suitable dielectric materials may also be used, provided they satisfy the following conditions:

E_C≥E_P≥E_D，

wherein E_PA value representing the young's modulus of the material forming the structural layers of the

sheets

15a, 15b (FR-4 in the example shown); e_DA value representing the young's modulus of the material (Kapton in the example shown) forming the dielectric layer 6; and E_CRepresenting the young's modulus of the material of the structure to be monitored, which in this embodiment is concrete with a typical young's modulus of 30 GPa.

It is also useful if the following further relationships are satisfied:

wherein α is a scaling factor, e.g., in the range of 1 to 2, e.g., equal to 1.25; and β is a corresponding scaling factor in the range of 8 to 11, e.g. equal to 9.6.

It is also emphasized that one or more capacitive sensors 1 can be advantageously used even in existing structures for monitoring the stresses acting in these structures, for example by making cuts or holes for inserting the capacitive sensors 1 in the structures.

The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.

Claims

1. A capacitive sensor designed to be introduced into a building structure to monitor stresses acting in the building structure, comprising:

a multilayer structure comprising:

an upper conductive layer defining an upper outer surface of the sensor and having a planar extension in a horizontal plane;

a lower conductive layer defining a lower outer surface of the sensor and having a planar extension in a horizontal plane, the upper and lower conductive layers being configured to be connected to a common reference potential to collectively define an electromagnetic screen for shielding the capacitive sensor from electromagnetic interference from outside the capacitive sensor;

at least a first structural layer of insulating material in contact with the upper conductive layer;

at least a second structural layer of insulating material in contact with the lower conductive layer;

at least a first slab layer made of a conductive material, said first structural layer of insulating material being interposed between said upper conductive layer and said first slab layer;

at least a second slab layer made of a conductive material, a second structural layer of insulating material being interposed between the lower conductive layer and the second slab layer; and

at least one dielectric layer interposed between said first plate layer and said second plate layer to define at least one detection capacitor inside said multilayer structure of said capacitive sensor,

wherein the detection capacitor is configured to detect a pressure acting on the capacitance sensor in a normal direction orthogonal to the horizontal plane, an

Wherein the detection capacitor further comprises: a plurality of standoffs coupled to at least one of the upper conductive layer and the lower conductive layer outside the multilayer structure of the capacitive sensor, wherein each standoff has:

a coupling portion configured to be coupled to a surface of the respective upper conductive layer or the lower conductive layer;

a body portion extending transversely to the surface of the respective upper or lower conductive layer; and

a head portion connected to and extending transversely to the body portion and substantially parallel to the surface of the respective upper or lower conductive layer,

wherein the bracket acts as an attachment element for attaching the capacitive sensor to the material of the building structure.

2. The sensor of claim 1, wherein the multilayer structure comprises at least a first and a second double-sided sheet, the first double-sided sheet defining the upper conductive layer, the first structural layer, and the first plate layer, and the second double-sided sheet defining the lower conductive layer, the second structural layer, and the second plate layer in the multilayer structure of the capacitive sensor.

3. The sensor of claim 2, wherein the materials forming the first and second structural layers and the dielectric layer satisfy the following relationship:

E_C≥E_P≥E_D，

wherein E_PA value representing the Young's modulus of the materials forming the first and second structural layers; e_DA value representing a Young's modulus of a material forming the dielectric layer; and E_CA Young's modulus of a material representing an architectural structure in which the capacitive sensor is configured to be embedded.

4. A sensor according to claim 3, wherein the following further relationship is also satisfied:

where α is a scaling factor in the range of 1 to 2 and β is a corresponding scaling factor in the range of 8 to 11.

5. The sensor of claim 1, wherein each of the first structural layer and the second structural layer is FR-4 and the dielectric layer is Kapton.

6. The sensor of claim 1, wherein the body portion of the support is shaped to: a parallelepiped; a trapezoid shape; a truncated pyramid; or a truncated cone.

7. The sensor of claim 1, wherein the support is configured to allow detection of tensile stress that creates a back pressure on the upper conductive layer and the lower conductive layer.

8. The sensor of claim 1, further comprising a support coupled laterally to the multilayer structure and transverse to a vertical direction of the stack of multilayer structures.

9. The sensor of claim 1, including a first trench formed at least through an entire thickness of the first plate layer to define and separate an active portion of the first plate layer inside the first trench and to define a first plate of the detection capacitor from an outer portion of the first plate layer outside the first trench.

10. The sensor of claim 9, further comprising a second trench formed at least through an entire thickness of the second plate layer to define and separate an active portion of the second plate layer inside the second trench and to define a second plate of the detection capacitor from an outer portion of the second plate layer outside the second trench; the active portions of the first and second plies collectively define an active detection region of the sensor.

11. A sensor according to claim 10, wherein the first plate of the detection capacitor has a dimension in a horizontal plane of a main extension of the first plate layer which is smaller than a dimension in the horizontal plane of the second plate of the corresponding detection capacitor.

12. The sensor of claim 11, wherein the active detection regions and the corresponding detection capacitors are capable of detecting a component of pressure acting on an upper outer surface of the upper conductive layer and/or on the surface of the lower conductive layer of the capacitive sensor in a direction normal to the surface, the sensor being insensitive to a component of the pressure parallel to the upper and lower outer surfaces.

13. The sensor of claim 10, wherein the first and second trenches each have a respective extension portion defining respective electrical connection portions in the first and second plate layers, respectively, the electrical connection portions extending from the active portion and reaching the outer portions of the first and second plate layers, respectively, the sensor further comprising electrical connection elements for connection to the respective electrical connection portions, the respective electrical connection elements configured to define first and second plate electrodes of the detection capacitor.

14. A sensor according to claim 13, wherein the electrical connection elements comprise respective connection holes plated on an inner wall, the connection holes extending from a surface of the upper and/or lower conductive layer and at least partially through the multilayer structure of the capacitive sensor and reaching the first and second plate layers, respectively, terminating at the electrical connection portions outside the active portions of the first and second plate layers, respectively.

15. The sensor of claim 14, wherein the connection element further comprises first and second electrical contact pads on the surface of at least one of the upper or lower conductive layers, the first and second electrical contact pads being in electrical contact with the connection aperture to allow making an electrical connection to a plate of the detection capacitor to define the first and second plate electrodes; wherein a third electrical contact pad is also disposed in a position adjacent to the first and second electrical contact pads and in electrical contact with the upper and lower conductive layers to define a shield electrode of the capacitive sensor.

16. The sensor of claim 10, further comprising a through-hole passing through an entire thickness of the multilayer structure and configured to allow fluid communication between the upper and lower outer surfaces of the capacitive sensor.

17. The sensor of claim 10, further comprising a plated through hole passing through an entire thickness of the multilayer structure and located along a lateral perimeter of the multilayer structure of the capacitive sensor; the plated through holes collectively define a shield against electromagnetic interference configured to laterally insulate and shield the detection capacitor formed inside the multilayer structure of the capacitive sensor.

18. The sensor of claim 10, further comprising a fastening through hole passing through an entire thickness of the multilayer structure of the capacitive sensor and positioned outside the active detection area, the fastening through hole configured to be joined to a building structure by a rigid and/or elastic or partially elastic connecting wire.

19. The sensor of claim 1, further comprising a further dielectric layer and a further slab layer configured to define at least one further detection capacitor configured to interact with the detection capacitor for detecting the stress.

20. A stress detection system comprising the capacitive sensor of claim 1, and an electronic measurement circuit coupled to the capacitive sensor to operate to process a corresponding detection signal indicative of the stress.